Heat exchanger

ABSTRACT

Rotary heat exchangers are formed with a core through which extend a plurality of passageway-defining tubes. The tubes are set at an angle to the axis of rotation and are partially filled with heat conductive elements. As the core rotates, the opposite ends of each of the tubes become respectively elevated or lowered with respect to the other end, and the elements thus gravitationally shift their relative position within the tubes as the core rotates. The shifting of the elements within the tubes permits a self-cleaning action. The elements themselves have low strength at high temperature, but are not required to carry any of the structural load. The employment of heat conductive elements provides a substantial surface area and permits the use of poor heat conductive material, such as stainless steel, for the core tube construction. Thus the passageway-defining tubes may be larger in cross section since the contained elements provide a large heat transfer action. The invention is shown as being applied to an axial heat exchanger and to a drum type (radial) heat exchanger.

ilited States Patent 1 Stalker, deceased [11.1 I 3,872,918 [4 1 Mar. 25, 1975 1 HEAT EXCHANGER [73] Assignee: The Stalker Corporation, Essexville,

Mich.

22 Filed: Feb. 21, 1974 21 Appl. No.: 444,401

[52] [1.5. CI 165/5, 165/8, 165/10 [51] Int. Cl. F28d 19/00 [58] Field 01 Search 165/8, 5, 1O

[56] References Cited UNITED STATES PATENTS 1,762,320 6/1930 Wood 165/5 2,183,936 12/1939 Karlsson et a1. 165/5 3,224,498 12/1965 Hochmuth 165/5 FOREIGN PATENTS OR APPLICATIONS 781,989 8/1957 United Kingdom 165/10 706,270 3/1935 Canada 165/10 621,722 11/1935 Germany 165/10 1,952,719 5/1971 Germany 165/5 Primary E.raminer-Albert W. Davis Attorney, Agent, or FirmBiebel, French & Bugg 57 ABSTRACT Rotary heat exchangers are formed with a core through which extend a plurality of passageway defining tubes. The tubes are set at an angle to the axis of rotation and are partially filled with heat conductive elements. As the core rotates, the opposite ends of each of the tubes become respectively elevated or lowered with respect to the other end, and the elements thus gravitationally shift their relative position within the tubes as the core: rotates. The shifting of the elements within the tubes permits a selfcleaning action. The elements themselves have low strength at high temperature, but are not required to carry any of the structural load. The employment of heat conductive elements provides a substantial surface area and permits the use of poor heat conductive material, such as stainless steel, for the core tube con ,struction. Thus the passageway-defining tubes may be larger in cross section since the contained elements provide a large heat transfer action. The invention is shown as being applied to an axial heat exchanger and to a drum type (radial) heat exchanger.

8 Claims, 6 Drawing Figures t A NYE U MAR 2 5 I975 FIG-5 FIG-4 HEAT EXCHANGER BACKGROUND OF THE INVENTION This invention is directed to the art of rotary heat exchangers such as those employed for recovering heat from exhaust gases of turbine engines or the like. A particular problem in such heat exchangers is that of the accumulation of the products of combustion within the small heat exchange passageways formed within the rotary drum or core. Various attempts have been made to solve the problem of accumulation of products of combustion with varying degrees of success. In Grames et al. US. Pat. No. 3,288,204 of I966 chains are loosely suspended from one wall forming the heat exchange medium and an impact device or trip hammer is periodically struck against the side of the drum to jar accumulated material loose from the chains. Another chain type heat exchanger directed to the cleaning problem is Hockmuth U.S. Pat. No. 3,224,498 of 1965 in which the direction of rotation of the drum is intermittently reversed so that sets of chains are alternately loosened or tightened to produce an agitation or flexing for the purpose of removing deposits of flyash on the chains.

SUMMARY OF THE INVENTION The heat exchanger of the present invention utilizes a core which is rotatable about an axis and a plurality of small passageways are formed in the core for the conduction of hot and cold gases therethrough. These passageways are defined by tubes which in one embodiment extend in the general axial direction but are inclined or skewed with respect to the axis of rotation. Thus, as the core rotates, one end of each passageway is alternately raised and lowered relative to the other.

In another embodiment the tubes extend radially so that the same effect is achieved.

The tubes are substantially but not completely filled with individual heat conductive elements, such as links of chain, pellets, shot, or the like. The elements are contained in each passageway substantially along the entire length of the passageway, but some open or free space is provided. The elements provide thereabout a tortuous space through which the gases may move from one end of the tube to the other while providing a large heat transfer surface. Since the elements have little or no mechanical or structural stress placed thereon, they may be formed of high conductive material which has poor mechanical strength at high temperature, such as copper or aluminum, while the strength of the core is contained in the tubes themselves.

The heat conductive elements move or shift in the tubes as the core is rotated, and as the ends of the respective tubes are alternately raised or lowered relative to their opposite ends. The shifting or moving of the elements provides a self-cleaning action. Also, the tubes may have a larger cross section than is customarily employed in heat passages for rotary heat exchangers, since the interior movable parts provide a large heat transfer action.

An important object of the invention is the provision of a rotary disc or drum type heat exchanger in which passages are defined by tubes which are at an angle to the axis of rotation and the passages are loosely filled with individual elements formed of high heat conductivity material.

Another object is the provision of a heat exchanger core in which axially inclined passages contain heat exchange elements which are free to move or shift with the rotation of the core to be self cleaning.

A further object of the invention is the provision of a rotary heat exchanger in which the core is comprised of a plurality of stainless steel tubular members or the like defining passageways through which hot and cold gases may flow as the core is rotated and in which the tubular members are substantially filled with movable or individual small heat conductive elements which are not subject to the mechanical or structural stresses on the core and of which are shiftable or movable as the core rotates, to be self-cleaning.

These and other objects and advantages will be apparent from the following description, the accompanying drawings, and the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows a disc-type rotary heat exchanger with the outer case partially broken away;

FIG. 2 is a transverse fragementary section through the case and the core taken generally along the line 22 of FIG. 1;

FIG. 3 is a side view of the core of FIG. 2;

FIG. 4 illustrates one ofthe tubes or passages isolated from the core, the tube being substantially filled with heat conductive pellets;

FIG. 5 is a view similar to FIG. 4 showing a core tube incorporating a loosely fitted chain in which the chain links are the heat conductive elements; and

FIG. 6 is a fragmentary view of a drum-type heat exchanger according to this invention.

DESCRIPTION OF PREFERRED EMBODIMENTS A heat exchanger constructed according to this invention is shown generally at 10 in FIG. 1 as including a case 12 and a disc-type heat exchange core 14 which is mounted for rotation on a shaft 116 journaled in bearings 20. The case includes a pair ofducts 22 and 24 for conducting hot fluid or gases into the core, and a pair of ducts 26 and 27 for conducting heated fluid or gases from the core. The fluids in the opposite ducts 22, 24 and 26, 27 are sealed from each other by the seals 30 and 32 which extend along the radial faces of the core 14 and by axially extending seals 34 and 36 at the opposite sides of the periphery of the core 14. Conventional seals may be used as disclosed for example in the patents of I-Iryniszak US. Pat. No. 3,209,8l3 of 1965 or Cox et al., U.S. Pat. No. 2,747,843 of 1956. Alternatively, a pressure seal may be used as shown in copending application Ser. No. 274,408 filed July 24, 1972, now abandoned.

The core 14 is formed with a plurality of relatively small passages leading from one radial face thereof generally in the axial direction to the-opposite radial face thereof to define a corresponding plurality of conduits for the conduction of the hot and cold gases. The passages are defined by individual tubes 40 which may have any cross sectional configuration. The tubes 40 are preferably disposed or skewed at an angle relative to the axis of rotation, as shown in phantom for the tube 42 in- FIGS. 3 and 4. The inclined rotation of the individual tubes 40 may be achieved by forming the core 14 with the tubes straight through and then twisting one axial end of the core with respect to the other axial end. Alternatively, the tubes can be formed to run on relatively straight inclined paths as shown for the tube 42, or they may follow curved paths. The purpose of setting or forming a tube at an angle to the axis of rotation is to cause first one and then the other end to be relatively elevated as the core is slowly rotated, so that the effect is that each tube 40 slopes alternately from one end to the other upon rotation of the core.

Each of the tubes 40, as illustrated by the tube 42 in FIG. 4 and the tube 42A of FIG. 5, is substantially completely filled with movable heat conductive elements. The elements are preferably small individual particles or parts formed of highly heat conductive material such as copper or aluminum. They may have a regular or irregular shape and examples include small balls, shot, pellets or the like such as shown at 43 in FIG. 4. Another example of suitable elements is copper wire which has been cut into short lengths. Interlocking elements may also be used and have the advantage of simplifying retention within the tubes. Thus, the interconnected chain links 43 A of FIG. 5 may be employed.

The elements whether they be pellets, links of chain, or the like, do not completely fill the tubes, thus forming a free space 44 in FIG. 4 and the spaces 44A of FIG. 5. inherently, the elements provide a relatively large surface area while presenting a tortuous path through which the air flows as the core is rotated. Heat'exchange cores are generally slowly rotated, in the order of -30 revolutions per minute. Thus, the pellets are primarily subject to gravitational action and since there is a free space provided, as the tubes 40 change in inclination, the elements are free to shift their position within their respective tubes and in this manner tend to be self-cleaning. Further, the force of the gases or air moving through the core tends to disperse and move the particles, since they are free to move, thus enhancing the cleaning action.

When small shot or other small loose particles are used as shown in 43 in FIG. 4, the ends ofthe tubes are closed by the perforated mesh or apertured closures to retain the pellets in the tubes and permit the flow of gases therethrough. Alternatively, the pellets can be retained in a metal mesh bag inserted in the tube and retained by a retainer pin, such as the retainer pin 52 which is used in the embodiment of FIG. 5 to retain the chain. A combination of such mesh bags of particles may be used at the ends with free pellets in thecenter of the tube, if desired. Where mesh bags are used, re-

' tainer pins 52 would be employed at the opposite ends of each tube. Where chain links 43 are used, since the links substantially fill the tubes 42A and cannot pass by each other, only a single retainer pin 52 need be used.

There is no structural stress on the heat exchange elements or particles. Accordingly, they may be formed of material which has low strength at high temperature. On the other hand, the core itself including the tubes may be formed of stainless steel for example, which is a relatively poor conductor of heat. By providing a highly efficient conducting material in the form of the elements 43, 43A, the efficiency of the heat exchanger is greatly enhanced. Also, the tubes 40 may have a larger cross sectional area than is customary with tube type heat exchangers, since the interior movable elements provide a large heat transfer action.

The invention is not limited in its application to axial or disc-type heat exchangers 14 as shown in FIGS. 1-3. Rather, it is equally useful for drum or radial type heat exchangers of the type shown, for example in Mondt U.S. Pat. No. 3,315,729 of 1967 and Gallagher U.S. Pat. No. 3,216,487 of 1965. In this case, the individual tubes would be arranged radially with respect to the drum, as illustrated by the tubes 42B of FIG. 6 extending between the perforated inner wall 55 and the perforated outer wall 56. The tubes themselves may extend in straight lines or may have tapered'walls as desired.

The operation of the heat exchangers of this invention is largely self-evident from the foregoing description. In the case of the axial unit 14, the drum will be rotated at a relatively slow rate so that the heat exchange elements pick up the heat from the gases in the duct 22 and transfer the same to the gases flowing in the duct 24. The direction of flow of gases may be in the same direction as shown by the arrows in FIG. 1 or they may be arranged in a counter flow direction. Counter'flow would have the additional advantage of subjecting the elements, such as the pellets, to the force of flow from opposite directions, enhancing the selfcleaning action.

As the core rotates the movable elements, such as the pellets 43 or the chain lines 43A, it will be subject to gravitational force and due to the relative inclination of the tubes 40 with respect to the axis of rotation, there will be a physical shifting of these elements within the tubes and they will tend to remain free of deposits.

With respect to the radial or drum embodiment of FIG. 6, it will be seen that the tubes 428 will be totally inverted as the drum turns and since a free space 44 is' provided as in the axial embodiment, the individual elements are thus permitted a limited shifting movement, thus enhancing the self-cleaning action.

It will therefore be seen that this invention provides efficient self-cleaning rotary heat exchangers which are high in efficiency and which may be manufactured at relative low cost.

While the forms of apparatus herein described constitutes preferred embodiments of the invention, it is to be understood that the invention is not limited to these precise forms of apparatus, and that changes may be made therein without departing from the scope of the invention.

What is claimed is:

1. A self-cleaning rotary heat exchanger in which a heat exchange core rotates through hot gas and cold gas ducts, the improvement in core construction comprising a plurality of passageways extending from one side of said core to the other for the passage of gases therethrough, said passageways being defined by a plurality of individual tubes which are inclined to the axis of rotation so that the ends thereof alternate in relative elevation as the core is rotated about its axis of rotation, a plurality of heat conductive elements partially filling each of said tubes leaving a free space therein so that said elements may shift in relative position within said tubes with the rotation of said core, and means retaining the elements in said tubes while providing for the flow of gases therethrough.

2. The heat exchanger of claim 1 in which said elements are formed of high heat conductive material such as copper or aluminum and said tubes are formed of stainless steel.

3. The heat exchanger of claim 1 in which said tubes extend in a generally axial direction.

4. The heat exchanger of claim 1 in which said tubes extend in a generally radial direction.

5. The heat exchanger of claim 1 in which said elements are pellets.

6. The heat exchanger of claim 1 in which said elements are interconnected chain links.

7. A self-cleaning rotary heat exchanger in which a heat exchange core rotates through hot gas and cold gas ducts, the improvement in core construction comprising a plurality of generally axially extending passageways extending from one axial side of said core to the other axial side for the passage of gases therethrough, said passageways being defined by a plurality of individual tubes which are skewed to the axis of rotation so that the ends thereof alternate in relative elevation as the core is rotated about its axis of rotation, a plurality of individual heat conductive elements substantially but not completely filling said tubes leaving a free space therein so that said elements are free to shift in relative position within said tubes with the rotation of said core, and means retaining the elements in said tubes while providing for the flow of gases therethrough.

8. A self-cleaning rotary heat exchanger in which a heat exchange core rotates through hot gas and cold gas ducts, the improvement in core construction comprising a plurality of generally axially extending passageways extending from one axial side of said core to the other axial side for the passage of gases therethrough, said passageways being defined by a plurality of individual tubes which are skewed to the axis of rotation so that the ends thereof alternate in relative elevation as the core is rotated about its axis of rotation, a plurality of heat conductive pellets substantially but not completely filling said tubes leaving a free space therein so that said pellets shift in relative position within said tubes with the rotation of said core, and means closing the ends of said tubes for retaining the pellets therein while providing for the flow of gases 

1. A self-cleaning rotary heat exchanger in which a heat exchange core rotates through hot gas and cold gas ducts, the improvement in core construction comprising a plurality of passageways extending from one side of said core to the other for the passage of gases therethrough, said passageways being defined by a plurality of individual tubes which are inclined to the axis of rotation so that the ends thereof alternate in relative elevation as the core is rotated about its axis of rotation, a plurality of heat conductive elements partially filling each of said tubes leaving a free space therein so that said elements may shift in relative position within said tubes with the rotation of said core, and means retaining the elements in said tubes while providing for the flow of gases therethrough.
 2. The heat exchanger of claim 1 in which said elements are formed of high heat conductive material such as copper or aluminum and said tubes are formed of stainless steel.
 3. The heat exchanger of claim 1 in which said tubes extend in a generally axial direction.
 4. The heat exchanger of claim 1 in which said tubes extend in a generally radial direction.
 5. The heat exchanger of claim 1 in which said elements are pellets.
 6. The heat exchanger of claim 1 in which said elements are interconnected chain links.
 7. A self-cleaning rotary heat exchanger in which a heat exchange core rotates through hot gas and cold gas ducts, the improvement in core construction comprising a plurality of generally axially extending passageways extending from one axial side of said core to the other axial side for the passage of gases therethrough, said passageways being defined by a plurality of individual tubes which are skewed to the axis of rotation so That the ends thereof alternate in relative elevation as the core is rotated about its axis of rotation, a plurality of individual heat conductive elements substantially but not completely filling said tubes leaving a free space therein so that said elements are free to shift in relative position within said tubes with the rotation of said core, and means retaining the elements in said tubes while providing for the flow of gases therethrough.
 8. A self-cleaning rotary heat exchanger in which a heat exchange core rotates through hot gas and cold gas ducts, the improvement in core construction comprising a plurality of generally axially extending passageways extending from one axial side of said core to the other axial side for the passage of gases therethrough, said passageways being defined by a plurality of individual tubes which are skewed to the axis of rotation so that the ends thereof alternate in relative elevation as the core is rotated about its axis of rotation, a plurality of heat conductive pellets substantially but not completely filling said tubes leaving a free space therein so that said pellets shift in relative position within said tubes with the rotation of said core, and means closing the ends of said tubes for retaining the pellets therein while providing for the flow of gases therethrough. 